The production of cyclic styrene carbonate from CO2 cycloaddition to styrene oxide, using tetrabutylammonium bromide (TBABr) as catalyst, was investigated. Two different reaction systems, a CO2-rich and an epoxide-rich were studied. Reactions were performed in a visual high pressure cell, at different temperatures (313.2, 333.2, and 353.2 K) and pressures (0.5-18 MPa). High pressure phase behaviour manipulation of the reaction system was explored to shift catalysis from homogeneous to heterogeneous, by changing operation conditions. Styrene carbonate formation was monitored quantitatively by using H-1 NMR spectroscopy. (C) 2015 Elsevier B.V. All rights reserved.